[kernel] Simplify mailbox code, and messages

A number of simplifications of mailboxes now that the interface is much
simpler, and synchronous.

* call and respond can now only transfer one handle at a time
* mailbox objects got rid of the message queue, and just have
  wait_queues of blocked threads, and a reply_to map.
* threads now have a message_data struct on them for use by mailboxes

definitions/objects/mailbox.def

@@ -19,7 +19,7 @@ object mailbox : object {
     method call [cap:send] {
         param tag uint64 [inout]
         param subtag uint64 [inout]
-        param handles ref object [inout list zero_ok]
+        param give_handle ref object [inout handle]
     }
 
     # Respond to a message sent using call, and wait for another
@@ -29,9 +29,8 @@ object mailbox : object {
     method respond [cap:receive] {
         param tag uint64 [inout]
         param subtag uint64 [inout]
-        param handles ref object [inout list zero_ok]
+        param give_handle ref object [inout handle]
-        param handles_in size
+        param reply_tag uint64 [inout]
-        param reply_tag uint16 [inout]
         param flags uint64
     }
 }

src/kernel/objects/mailbox.cpp

@@ -3,16 +3,8 @@
 #include "objects/mailbox.h"
 #include "objects/thread.h"
 
-DEFINE_SLAB_ALLOCATOR(obj::mailbox::message);
-
 namespace obj {
 
-static_assert(mailbox::message::slab_size % sizeof(mailbox::message) == 0,
-        "mailbox message size does not fit cleanly into N pages.");
-
-constexpr uint64_t no_message = 0;
-constexpr uint64_t has_message = 1;
-
 mailbox::mailbox() :
     kobject(kobject::type::mailbox),
     m_closed {false},
@@ -28,91 +20,80 @@ mailbox::~mailbox()
 void
 mailbox::close()
 {
-    util::scoped_lock lock {m_message_lock};
-
     // If this was previously closed, we're done
-    if (closed()) return;
+    bool was_closed = __atomic_exchange_n(&m_closed, true, __ATOMIC_ACQ_REL);
-    m_closed = true;
+    if (was_closed) return;
 
-    while (!m_messages.empty()) {
+    m_callers.clear(j6_status_closed);
-        message *msg = m_messages.pop_front();
+    m_responders.clear(j6_status_closed);
-        delete msg;
-    }
-
-    for (auto &p : m_pending) {
-        delete p.val.msg;
-    }
-    m_queue.clear();
 }
 
-bool
+j6_status_t
-mailbox::call(message *msg)
+mailbox::call()
 {
-    uint16_t reply_tag = next_reply_tag();
+    if (closed())
+        return j6_status_closed;
 
-    util::scoped_lock lock {m_message_lock};
-
-    msg->reply_tag = reply_tag;
     thread &current = thread::current();
-    m_pending.insert(reply_tag, {&current, msg});
+    m_callers.add_thread(&current);
 
-    m_messages.push_back(msg);
+    thread *responder = m_responders.pop_next();
+    if (responder)
+        responder->wake(j6_status_ok);
 
-    thread *t = m_queue.pop_next();
+    return current.block();
-
-    lock.release();
-    if (t) t->wake(has_message);
-
-    uint64_t result = current.block();
-    return result == has_message;
 }
 
-bool
+j6_status_t
-mailbox::receive(mailbox::message *&msg, bool block)
+mailbox::receive(thread::message_data &data, reply_tag_t &reply_tag, bool block)
 {
-    util::scoped_lock lock {m_message_lock};
+    if (closed())
+        return j6_status_closed;
 
-    // This needs to be a loop because we're re-acquiring the lock
+    thread &current = thread::current();
-    // after waking up, and may have missed the message that woke us
+    thread *caller = nullptr;
-    while (m_messages.empty()) {
-        if (!block) {
-            msg = nullptr;
-            return false;
-        }
 
-        thread &cur = thread::current();
+    while (true) {
-        m_queue.add_thread(&cur);
+        caller = m_callers.pop_next();
+        if (caller)
+            break;
 
-        lock.release();
+        if (!block)
-        uint64_t result = cur.block();
+            return j6_status_would_block;
-        if (result == no_message)
+
-            return false;
+        m_responders.add_thread(&current);
-        lock.reacquire();
+        j6_status_t s = current.block();
+        if (s != j6_status_ok)
+            return s;
     }
 
-    msg = m_messages.pop_front();
+    util::scoped_lock lock {m_reply_lock};
-    return true;
+    reply_tag = ++m_next_reply_tag;
+    m_reply_map.insert({ reply_tag, caller });
+    lock.release();
+
+    data = caller->get_message_data();
+    return j6_status_ok;
 }
 
-mailbox::replyer
+j6_status_t
-mailbox::reply(uint16_t reply_tag)
+mailbox::reply(reply_tag_t reply_tag, const thread::message_data &data)
 {
-    util::scoped_lock lock {m_message_lock};
+    if (closed())
+        return j6_status_closed;
 
-    pending *p = m_pending.find(reply_tag);
+    util::scoped_lock lock {m_reply_lock};
-    if (!p) return {};
+    reply_to *rt = m_reply_map.find(reply_tag);
+    if (!rt)
+        return j6_err_invalid_arg;
 
-    thread *caller = p->sender;
+    thread *caller = rt->thread;
-    message *msg = p->msg;
+    m_reply_map.erase(reply_tag);
-    m_pending.erase(reply_tag);
+    lock.release();
 
-    return {msg, caller, has_message};
+    caller->get_message_data() = data;
-}
+    caller->wake(j6_status_ok);
-
+    return j6_status_ok;
-mailbox::replyer::~replyer()
-{
-    if (caller)
-        caller->wake(status);
 }
 
 } // namespace obj

src/kernel/objects/mailbox.h

@@ -4,11 +4,13 @@
 
 #include <j6/cap_flags.h>
 #include <util/counted.h>
-#include <util/map.h>
+#include <util/node_map.h>
 #include <util/spinlock.h>
 
+#include "heap_allocator.h"
 #include "memory.h"
 #include "objects/kobject.h"
+#include "objects/thread.h"
 #include "slab_allocated.h"
 #include "wait_queue.h"
 
@@ -21,6 +23,8 @@ class mailbox :
     public kobject
 {
 public:
+    using reply_tag_t = uint64_t;
+
     /// Capabilities on a newly constructed mailbox handle
     constexpr static j6_cap_t creation_caps = j6_cap_mailbox_all;
 
@@ -29,8 +33,6 @@ public:
     /// Max message handle count
     constexpr static size_t max_handle_count = 5;
 
-    struct message;
-
     mailbox();
     virtual ~mailbox();
 
@@ -38,88 +40,45 @@ public:
     void close();
 
     /// Check if the mailbox has been closed
-    inline bool closed() const { return m_closed; }
+    inline bool closed() const { return __atomic_load_n(&m_closed, __ATOMIC_ACQUIRE); }
 
     /// Send a message to a thread waiting to receive on this mailbox, and block the
-    /// current thread awaiting a response. The response will be placed in the message
+    /// current thread awaiting a response. The message contents should be in the calling
-    /// object provided.
+    /// thread's message_data.
-    /// \arg msg      [inout] The mailbox::message to send, will contain the response afterward
+    /// \returns      j6_status_ok if a reply was received
-    /// \returns      true if a reply was recieved
+    j6_status_t call();
-    bool call(message *msg);
 
     /// Receive the next available message, optionally blocking if no messages are available.
-    /// \arg msg          [out] a pointer to the received message. The caller is responsible for
+    /// \arg data         [out] a thread::message_data structure to fill
-    ///                   deleting the message structure when finished.
+    /// \arg reply_tag    [out] the reply_tag to use when replying to this message
     /// \arg block        True if this call should block when no messages are available.
-    /// \returns          True if a message was received successfully.
+    /// \returns          j6_status_ok if a message was received
-    bool receive(message *&msg, bool block);
+    j6_status_t receive(thread::message_data &data, reply_tag_t &reply_tag, bool block);
-
-    class replyer;
 
     /// Find a given pending message to be responded to. Returns a replyer object, which will
     /// wake the calling thread upon destruction.
     /// \arg reply_tag  The reply tag in the original message
-    /// \returns        A replyer object contining the message
+    /// \arg data       Message data to pass on to the caller
-    replyer reply(uint16_t reply_tag);
+    /// \returns        j6_status_ok if the reply was successfully sent
+    j6_status_t reply(reply_tag_t reply_tag, const thread::message_data &data);
 
 private:
-    inline uint16_t next_reply_tag() {
+    wait_queue m_callers;
-        return (__atomic_add_fetch(&m_next_reply_tag, 1, __ATOMIC_SEQ_CST) << 1) | 1;
+    wait_queue m_responders;
-    }
+
+    struct reply_to { reply_tag_t reply_tag; thread *thread; };
+    using reply_map =
+        util::node_map<uint64_t, reply_to, 0, heap_allocated>;
+
+    util::spinlock m_reply_lock;
+    reply_map m_reply_map;
 
     bool m_closed;
-    uint16_t m_next_reply_tag;
+    reply_tag_t m_next_reply_tag;
 
-    util::spinlock m_message_lock;
+    friend reply_tag_t & get_map_key(reply_to &rt);
-    util::deque<message*> m_messages;
-
-    struct pending { thread *sender; message *msg; };
-    util::map<uint16_t, pending> m_pending;
-    wait_queue m_queue;
 };
 
-
+inline mailbox::reply_tag_t & get_map_key(mailbox::reply_to &rt) { return rt.reply_tag; }
-struct mailbox::message :
-    public slab_allocated<message, mem::frame_size>
-{
-    uint64_t tag;
-    uint64_t subtag;
-
-    uint16_t reply_tag;
-    uint8_t handle_count;
-
-    j6_handle_t handles[mailbox::max_handle_count];
-};
-
-class mailbox::replyer
-{
-public:
-    replyer() : msg {nullptr}, caller {nullptr}, status {0} {}
-    replyer(mailbox::message *m, thread *c, uint64_t s) : msg {m}, caller {c}, status {s} {}
-    replyer(replyer &&o) : msg {o.msg}, caller {o.caller}, status {o.status} {
-        o.msg = nullptr; o.caller = nullptr; o.status = 0;
-    }
-
-    replyer & operator=(replyer &&o) {
-        msg = o.msg; caller = o.caller; status = o.status;
-        o.msg = nullptr; o.caller = nullptr;
-        return *this;
-    }
-
-    /// The replyer's dtor will wake the calling thread
-    ~replyer();
-
-    /// Check if the reply is valid
-    inline bool valid() const { return msg && caller; }
-
-    /// Set an error to give to the caller
-    inline void error(uint64_t e) { status = e; }
-
-    mailbox::message *msg;
-
-private:
-    thread *caller;
-    uint64_t status;
-};
 
 } // namespace obj

src/kernel/objects/thread.h

@@ -114,6 +114,14 @@ public:
     /// \returns  The clock time at which to wake. 0 for no timeout.
     inline uint64_t wake_timeout() const { return m_wake_timeout; }
 
+    struct message_data
+    {
+        uint64_t tag, subtag;
+        j6_handle_t handle;
+    };
+
+    message_data & get_message_data() { return m_message_data; }
+
     inline bool has_state(state s) const {
         return static_cast<uint8_t>(m_state) & static_cast<uint8_t>(s);
     }
@@ -186,6 +194,7 @@ private:
 
     uint64_t m_wake_value;
     uint64_t m_wake_timeout;
+    message_data m_message_data;
 
     j6_handle_t m_self_handle;
 };

src/kernel/syscalls/helpers.h

@@ -37,6 +37,12 @@ j6_status_t get_handle(j6_handle_t id, j6_cap_t caps, T *&object)
     return j6_status_ok;
 }
 
+template <typename T>
+inline j6_status_t get_handle(j6_handle_t *id, j6_cap_t caps, T *&object)
+{
+    return get_handle<T>(*id, caps, object);
+}
+
 template <>
 inline j6_status_t get_handle<obj::kobject>(j6_handle_t id, j6_cap_t caps, obj::kobject *&object)
 {

src/kernel/syscalls/mailbox.cpp

@@ -27,78 +27,29 @@ mailbox_close(mailbox *self)
     return j6_status_ok;
 }
 
-j6_status_t
-prep_send(
-        mailbox::message *msg,
-        uint64_t tag,
-        uint64_t subtag,
-        const j6_handle_t *handles,
-        size_t handle_count)
-{
-    if (!msg ||
-        handle_count > mailbox::max_handle_count)
-        return j6_err_invalid_arg;
-
-    msg->tag = tag;
-    msg->subtag = subtag;
-
-    msg->handle_count = handle_count;
-    memcpy(msg->handles, handles, sizeof(j6_handle_t) * handle_count);
-
-    return j6_status_ok;
-}
-
-void
-prep_receive(
-        mailbox::message *msg,
-        uint64_t *tag,
-        uint64_t *subtag,
-        uint16_t *reply_tag,
-        j6_handle_t *handles,
-        size_t *handle_count)
-{
-    if (tag) *tag = msg->tag;
-    if (subtag) *subtag = msg->subtag;
-    if (reply_tag) *reply_tag = msg->reply_tag;
-
-    *handle_count = msg->handle_count;
-    process &proc = process::current();
-    for (size_t i = 0; i < msg->handle_count; ++i) {
-        proc.add_handle(msg->handles[i]);
-        handles[i] = msg->handles[i];
-    }
-}
-
 j6_status_t
 mailbox_call(
         mailbox *self,
         uint64_t *tag,
         uint64_t *subtag,
-        j6_handle_t *handles,
+        j6_handle_t *handle)
-        size_t *handle_count)
 {
-    mailbox::message *msg = new mailbox::message;
+    thread::message_data &data =
+        thread::current().get_message_data();
 
-    j6_status_t s = prep_send(msg,
+    data.tag = *tag;
-            *tag, *subtag,
+    data.subtag = *subtag;
-            handles, *handle_count);
+    data.handle = *handle;
 
-    if (s != j6_status_ok) {
+    j6_status_t s = self->call();
-        delete msg;
+    if (s != j6_status_ok)
         return s;
-    }
 
-    if (!self->call(msg)) {
+    *tag = data.tag;
-        delete msg;
+    *subtag = data.subtag;
-        return self->closed() ? j6_status_closed :
+    *handle = data.handle;
-               j6_err_unexpected;
+    process::current().add_handle(*handle);
-    }
 
-    prep_receive(msg,
-            tag, subtag, 0,
-            handles, handle_count);
-
-    delete msg;
     return j6_status_ok;
 }
 
@@ -107,46 +58,27 @@ mailbox_respond(
         mailbox *self,
         uint64_t *tag,
         uint64_t *subtag,
-        j6_handle_t *handles,
+        j6_handle_t *handle,
-        size_t *handle_count,
+        uint64_t *reply_tag,
-        size_t handles_in,
-        uint16_t *reply_tag,
         uint64_t flags)
 {
+    thread::message_data data { *tag, *subtag, *handle };
+
     if (*reply_tag) {
-        mailbox::replyer reply = self->reply(*reply_tag);
+        j6_status_t s = self->reply(*reply_tag, data);
-        if (!reply.valid())
+        if (s != j6_status_ok)
-            return j6_err_invalid_arg;
-
-        j6_status_t s = prep_send(reply.msg, *tag, *subtag,
-                handles, handles_in);
-
-        if (s != j6_status_ok) {
-            reply.error(s);
             return s;
-        }
     }
 
-
-    if (*handle_count < mailbox::max_handle_count)
-        return j6_err_insufficient;
-
-    mailbox::message *msg = nullptr;
-
     bool block = flags & j6_mailbox_block;
-    if (!self->receive(msg, block)) {
+    j6_status_t s = self->receive(data, *reply_tag, block);
-        // No message received
+    if (s != j6_status_ok)
-        return self->closed() ? j6_status_closed :
+        return s;
-               !block ? j6_status_would_block :
-               j6_err_unexpected;
-    }
 
-    prep_receive(msg,
+    *tag = data.tag;
-            tag, subtag, reply_tag,
+    *subtag = data.subtag;
-            handles, handle_count);
+    *handle = data.handle;
-
+    process::current().add_handle(*handle);
-    if (*reply_tag == 0)
-        delete msg;
 
     return j6_status_ok;
 }

src/kernel/wait_queue.cpp

@@ -43,11 +43,11 @@ wait_queue::pop_next_unlocked()
 }
 
 void
-wait_queue::clear()
+wait_queue::clear(uint64_t value)
 {
     util::scoped_lock lock {m_lock};
     for (auto *t : m_threads) {
-        if (!t->exited()) t->wake();
+        if (!t->exited()) t->wake(value);
         t->handle_release();
     }
 }

src/kernel/wait_queue.h

@@ -38,7 +38,8 @@ public:
     util::spinlock & get_lock() { return m_lock; }
 
     /// Wake and clear out all threads.
-    void clear();
+    /// \arg value  The value passed to thread::wake
+    void clear(uint64_t value = 0);
 
 private:
     /// Get rid of any exited threads that are next
@@ -46,6 +47,6 @@ private:
     void pop_exited();
 
     util::spinlock m_lock;
-    util::deque<obj::thread*, 8> m_threads;
+    util::deque<obj::thread*, 6> m_threads;
 };
 

src/libraries/util/util/deque.h

@@ -11,11 +11,11 @@ namespace util {
 template <typename T, unsigned N = 16>
 class deque
 {
+public:
     struct node { T items[N]; };
     using list_type = linked_list<node>;
     using node_type = typename list_type::item_type;
 
-public:
     class iterator
     {
     public:

src/user/drv.uart/main.cpp

@@ -61,10 +61,7 @@ channel_pump_loop()
 
     uint64_t tag = j6_proto_sl_register;
     uint64_t proto_id = "jsix.protocol.stream.ouput"_id;
-    size_t handle_count = 1;
+    result = j6_mailbox_call(slp, &tag, &proto_id, &cout_write);
-    result = j6_mailbox_call(slp,
-            &tag, &proto_id,
-            &cout_write, &handle_count);
     if (result != j6_status_ok)
         return 4;
 

src/user/srv.init/service_locator.cpp

@@ -25,23 +25,17 @@ service_locator_start(j6_handle_t mb)
 
     uint64_t tag = 0;
     uint64_t subtag = 0;
-    uint16_t reply_tag = 0;
+    uint64_t reply_tag = 0;
-
-    j6_handle_t handles[10] = {0};
-    const size_t handles_capacity = sizeof(handles)/sizeof(j6_handle_t);
-    size_t handles_count = 0;
 
+    j6_handle_t give_handle = j6_handle_invalid;
     uint64_t proto_id;
 
     while (true) {
-        size_t handles_in = handles_count;
+        j6_status_t s = j6_mailbox_respond(mb, &tag, &subtag, &give_handle,
-        handles_count = handles_capacity;
+                &reply_tag, j6_mailbox_block);
 
-        j6_status_t s = j6_mailbox_respond(mb,
+        if (s != j6_status_ok)
-                &tag, &subtag,
+            while (1);
-                handles, &handles_count,
-                handles_in, &reply_tag,
-                j6_mailbox_block);
 
         handle_entry *found = nullptr;
 
@@ -49,22 +43,21 @@ service_locator_start(j6_handle_t mb)
         case j6_proto_base_get_proto_id:
             tag = j6_proto_base_proto_id;
             subtag = j6_proto_sl_id;
-            handles_count = 0;
+            give_handle = j6_handle_invalid;
             break;
 
         case j6_proto_sl_register:
             proto_id = subtag;
-            if (handles_count != 1) {
+            if (give_handle == j6_handle_invalid) {
                 tag = j6_proto_base_status;
                 subtag = j6_err_invalid_arg;
-                handles_count = 0;
                 break;
             }
 
-            services.insert( {proto_id, handles[0]} );
+            services.insert( {proto_id, give_handle} );
             tag = j6_proto_base_status;
             subtag = j6_status_ok;
-            handles_count = 0;
+            give_handle = j6_handle_invalid;
             break;
 
         case j6_proto_sl_find:
@@ -72,18 +65,16 @@ service_locator_start(j6_handle_t mb)
             tag = j6_proto_sl_result;
 
             found = services.find(proto_id);
-            if (found) {
+            if (found)
-                handles_count = 1;
+                give_handle = found->handle;
-                handles[0] = found->handle;
+            else
-            } else {
+                give_handle = j6_handle_invalid;
-                handles_count = 0;
-            }
             break;
 
         default:
             tag = j6_proto_base_status;
             subtag = j6_err_invalid_arg;
-            handles_count = 0;
+            give_handle = j6_handle_invalid;
             break;
         }
     }

src/user/srv.logger/main.cpp

@@ -125,13 +125,11 @@ main(int argc, const char **argv)
     for (unsigned i = 0; i < 100; ++i) {
         uint64_t tag = j6_proto_sl_find;
         uint64_t proto_id = "jsix.protocol.stream.ouput"_id;
-        size_t handle_count = 0;
 
-        j6_status_t s = j6_mailbox_call(slp, &tag,
+        j6_status_t s = j6_mailbox_call(slp, &tag, &proto_id, &cout);
-                &proto_id, &cout, &handle_count);
         if (s == j6_status_ok &&
             tag == j6_proto_sl_result &&
-            handle_count == 1)
+            cout != j6_handle_invalid)
             break;
 
         cout = j6_handle_invalid;